1 Field of the Invention
The present invention relates to a display and, more particularly, to a wide band horizontal size regulation circuit which is selectively switched according to input frequencies, to control the value of current fed back, thereby adjusting the horizontal size of the display.
2 Detailed Description of Related Art
A display is a typical peripheral device of a computer, which displays a signal sent from the computer as an image, to allow a user to recognize it.
The display typically includes a video card, contained within a computer for providing a video signal, horizontal and vertical synchronous signals which are required for forming an image, a microcomputer for receiving the horizontal and vertical synchronous signals form the video card and for generating a picture control signal for controlling the monitor picture, vertical and horizontal deflection circuits for receiving the horizontal and vertical synchronous signals and for performing horizontal and vertical deflections to enable an electron beam generated by an electron gun of a CRT to be sequentially deflected starting from the top of the left portion of the CRT proceeding to the bottom of its right portion by a deflection yoke so as to form an image comprising a picture, a high voltage circuit for supplying a high voltage to the anode of the CRT using a blanking pulse generated by an output of the horizontal deflection circuit, a video preamplifier for amplifying a low-level image signal transmitted from the video card and a video main amplifier for amplifying the signal amplified by the video pre-amplifier.
The horizontal deflection circuit includes a horizontal oscillator circuit, horizontal drive circuit, a horizontal output circuit, and a horizontal size regulation circuit.
The horizontal output circuit and horizontal size regulation circuit include the microcomputer for generating a horizontal size control signal, a pulse width modulation IC for varying the width of a pulse for controlling the horizontal size according to the control signal generated by the microcomputer, a deflection controller for controlling the amount of current which flows through the choke coil of the horizontal output circuit, a current sensor for sensing the horizontal flyback pulse from the choke coil of the horizontal output circuit to provide it to the PWM-IC, a horizontal yoke for receiving the sawtooth wave output current from the horizontal output circuit and for providing deflection power and a linearity circuit and S-correction circuit which operate by a control signal from the microcomputer according to an input frequency.
The horizontal output circuit and horizontal size regulation circuit include the deflection controller containing a transformer and field effect transistor and various resistors.
Also included is a current sensor consisting of a diode and resistor capacitor combination for sensing and rectifying and smoothing the horizontal flyback pulse from a chopper coil of the horizontal output circuit and for transmitting the sensed voltage to the PWM-IC.
The operation of such a size regulation circuit is as follows. The on/off time of the field effect transistor is controlled according to a pulse width regulation signal output from the PWM-IC. The transistor is turned on during the on time of a pulse supplied from the transformer and turned off during its off time. Accordingly, the chopper coil of the horizontal output circuit is charged during the turned on time of the transistor and discharged during its turned off time, generating the horizontal flyback pulse. However, the size regulation voltage is fed back from the chopper coil to control the size. Thus, the detection value varies with the tolerance of the chopper coil and furthermore, the horizontal size regulation circuit can not adequately meet input frequency modes presently used with various computer systems.